Maternal Serum Ferritin Levels in Third Trimester and Risk of Small for Gestational Age in Northern Thailand: Implications for Management in Pregnancy

<b>Background:</b> Iron deficiency anemia is a recognized pregnancy risk, but excessive iron may also have adverse effects. Few studies, particularly in Asian populations, have examined elevated maternal ferritin in relation to birth outcomes. <b>Objectives</b>: To investigate the dose-response relationships between maternal serum ferritin concentrations in late pregnancy and birth outcomes, including preterm birth, small for gestational age (SGA), and placental characteristics. <b>Methods</b>: A retrospective study of 362 mother-infant pairs were analyzed. Maternal serum ferritin levels measured at 30-34 weeks' gestation were divided into quintiles, using 30.1-43.0 µg/L as the reference. Logistic and linear regression models were applied to examine associations with preterm birth, SGA, and placental indices. <b>Results</b>: Preterm birth rates ranged 7.3-18.8% across ferritin quintiles, but no significant association was observed. In contrast, SGA prevalence increased from 20.8% to 47.2% (<i>p</i>-trend = 0.001). Women in the highest ferritin quintile had 3.31-fold higher adjusted odds of SGA (95% CI: 1.51-7.28, <i>p</i> = 0.003). Each SD increase in ferritin corresponded to 31% higher odds of SGA (OR = 1.31, 95% CI: 1.01-1.71). Elevated ferritin (>43.0 µg/L) was also associated with reduced placental weight (<415 g) (adjusted OR = 3.02, 95% CI: 1.61-5.69, <i>p</i> = 0.001). <b>Conclusions</b>: Increasing maternal ferritin levels in the third trimester were associated with a dose-dependent rise in SGA risk and reduced placental weight. These findings suggest that excessive iron status may adversely influence placental function and fetal growth, underscoring the need for individualized nutrition management during pregnancy.